1. Field of the Invention:
This invention relates generally to a confinement device for a nuclear fusion plasma and more particularly to a polytron confinement device for a nuclear fusion plasma having an ion or plasma injection system.
2. Description of the Prior Art
It has been generally accepted that nuclear fusion as a power source holds great promise and may eventually even solve the energy problems of the world. A workable power system using this energy source has thus far eluded scientists and engineers, largely due to the problems of containment of the fusion material. In order to obtain a self-sustaining reaction, it is necessary to heat the fusion material to a very high temperature. At this temperature all material becomes a plasma of charged ions and electrons which is difficult to contain. Traditional solid walls are unable to hold such a plasma since any wall material would be vaporized instantly by the high temperatures and become part of the plasma.
A viable solution to this problem is a magnetic confinement. One particular type is the Tokamak. It consists of a torus in which a strong circular vacuum magnetic field along the torus is created by current carrying coils, encircling the torus. This magnetic field alone cannot confine the plasma, but a current, which flows along the magnetic field lines has to be induced in the plasma, which produces helically twisted magnetic field lines, which keep the plasma away from solid walls. A description of this may be found in an article by H. P. Furth entitled "The Tokamak" in Fusions, Academic Press volume 1 part A at page 103. While many devices have been built using this principle, none have yet progressed to the point of a usable self sustaining reaction.
Another device that has been suggested is the Polytron apparatus, described by M. G. Haines in Nuclear Fusion, 17, page 811, (1977) and M. Rhodes et al in Physical Review Letters, 48, page 1821, (1982), and shown generally as 10 in FIG. 1. Externally, this device resembles the Tokamak in that a toroidal vacuum centered track 12 has circular coils 14 surrounding cross sections of the torus. In this device, however, as seen in FIG. 2 adjacent coils 14 carry currents in opposite directions so that the magnetic field lines 18 form a circular line cusp parallel to the circular coils and halfway between adjacent coils. When a charged particle beam travels through the device, it tends to follow the axis of the torus since any divergence of the beam moves the particles into a strong magnetic field near the coils. This creates a focusing effect similar to that known in electron microscopy. (See W. Glaser "Elctronen-und Ionenoptik, Vol. XXXIII Korpuskularoptic", Handbuch der Physik). The configuration has the advantage that all the magnetic field lines are curved away from the plasma. This provides magnetohydrodynamic stability for the configuration, as described by N. A. Krall and A. W. Trivelpiece in Principles of Plasma Physics (1973) chapters 5 and 12.
Experiments have been performed using this configuration for several years. One such recent experiment had a large radius of the vacuum container torus of 45 cm., a plasma with an ion temperature of 40 eV and an accelerated ion lifetime of 140 microseconds. FIG. 3 indicates the position of the magnetic fields formed in this device. An iron core transducer 20 was used to induce an electric field to drive the beam. While this experiment worked well, the plasma duration and ohmic heating was limited by the Volt-Second rating of the transformer. It would be preferable to control plasma density, rotation speed of the plasma, temperature of the plasma and the duration of plasma containment independently of each other.